The Minuteman I was deactivated in 1972 when the Air Force began its modernization process to the Minuteman III.
The Air Force secured approval from the Department of Defense on 27 February 1958 to develop the Minuteman. From its very inception, the Minuteman program was oriented towards mass production of a simple, efficient, and highly survivable ICBM capable of destroying all types of enemy targets with consistent reliability. The Air Force hoped that such a program would reverse the unfavorable trend towards succeeding generations of progressively more costly ICBMs and provide the Strategic Air Command with a weapon system that was inexpensive to operate and maintain.
During the early development phase of Minuteman, the Strategic Air Command favored the concept of deploying at least a portion of the programmed force (from 50 to 150 ICBMs) on railroad cars. SAC submitted a requirement to the Air Staff on 12 February 1959 calling for the first mobile Minuteman unit to be operational no later than January 1963. To determine the feasibility of deploying Minuteman ICBMs on mobile launchers, SAC ordered a series of tests to be conducted, nicknamed "Operation Big Star." Beginning 20 June 1960, a modified test train, operating out of Hill Air Force Base, Utah, traveled across the western and central United States so technicians could study factors such as the ability of the nation's railroads to support mobile missile trains; problems associated with command, control, and communications; the effect of vibration on sensitive missiles and launch equipment; and human factors involved in the operation of a mobile missile system. Originally, six trial runs were projected, but only four were necessary to realize all test objectives. On 27 August 1960, the last of four Minuteman ICBM test trains arrived back at Hill AFB and the Air Force announced that the test of the Minuteman mobility concept had been completed satisfactorily.
Despite SAC's repeated pleas in favor of mobile Minuteman, the Air Force assigned top priority to the fixed silo-based Minuteman concept. Furthermore, on 28 March 1961, President John F. Kennedy deferred further action on the development of the three mobile Minuteman squadrons in favor of three additional squadrons of silo-based Minuteman units. Secretary of Defense Robert S. McNamara finally settled the issue on 7 December 1961 when he canceled the mobile Minuteman development program.
A decision regarding the final size of the silo-based Minuteman ICBM force was not made until December 1964. A new Minuteman system program directive issued on 11 December 1964 established the final Minuteman force at 1,000 missiles. Three years earlier, on 1 December 1961, Headquarters SAC had activated the first Minuteman squadron, the 10th Strategic Missile Squadron (ICBM-Model A Minuteman I) at Malmstrom Air Force Base, Montana. Only two other model "A" ICBM squadrons were activated by Headquarters SAC. These were the 12th Strategic Missile Squadron, activated on 1 March 1962, and the 490th Strategic Missile Squadron, activated on 1 May 1962, also located at Malmstrom. The next thirteen Minuteman squadrons activated by the Strategic Air Command were all model "B" Minuteman I units.
Strategic Air Command housed each Minuteman I, whether a model "A" or "B", in an unmanned, hardened, and widely-dispersed (three-to-seven mile intervals) underground-silo launch facility. A missile combat crew of two officers stationed in a hardened, underground launch control center monitored each flight of 10 launch facilities (five flights per squadron). For purposes of command, control, and communications, hardened underground cables linked all five launch control centers of a Minuteman squadron.
The Minuteman Force Modernization Program initiated in 1966 to replace all Minuteman I's with either Minuteman II's or Minuteman III's continued through the latter 1960s and into the mid-70s. The last Minuteman I series "An missiles were removed from their launch facilities at Malmstrom AFB, Montana, on 12 February 1969. These facilities were refurbished and outfitted with Minuteman II series "F" missiles. Boeing Aerospace Company, the contractor responsible for remodeling the launch facilities, completed the nine year modernization effort on 26 January 1975 when it turned over to SAC the last flight of ten Minuteman III missiles at the 90th Strategic Missile Wing, F.E. Warren AFB, Wyoming.